The shells and the end and/or middle pieces of such circular piston combustion engines have heretofore been fabricated as castings. The shell has consisted of a light metal casting, because its fabrication in cast iron, owing to comparatively low heat conductivity, resulted in excessive wall temperatures. An aluminum casting, however, is comparatively expensive, even if it can be produced by pressure casting. Furthermore, this comparatively soft material requires coating of the bearing surface with a hard material, the application and subsequent finishing of which is costly and time consuming.